Magnetic materials



Patented Aug. 14, 1945 MAGNETIC MATERIAL an a Nesbitt llrooklyn, N. r., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York so Drawing. Application Qctober 23,1941,

Serial No. 41am v '1 Claims. (01. 17 5-21) This invention relates to permanent magnet alloys and to magnets. produwd therefrom which This produces dispersion hardening in the mate- 'rial and produces aivery eilectlve permanent are caused to have more desirable properties as permanent magnets by a cold working treatment.

The invention also relates to and includes methods of treating and producing such improved alloys and. permanent magnets. I

An object of the invention is the production of better and more emcient permanent magnet Reduction of thickness by such rolling of a metal sheet as permits the material to spread laterally is only partially effective,

The evidence is that materials oi or produced according to the present invention generally are anisotropic and their improved properties are manifested chiefly in the direction in which the elongation takes place.

in the Patent No. 2,298,225 ity is pointed out that there are classes of materials which, it maintained at a certain high temperature but below the melting point, assume a form known as the "gamma" phase, and ii the material is thereafter cooled to around room temperature, it tends to assume the "alpha phase and thereafter it maintained at around 500 C. to 800 0., a; finely dispersed small amount of the "germ-ha phase forms in the alpha phase. This brief statement is to be read in the light of the information, diagrams, and discussion of said copending application.

As. pointed out in my Patent No. 2,298,225, dated October 6, 1942, 'a suitable procedure for preparing permanent magnet material is to melt the material and cool it to room temperature to produce formation of the "alpha phase and thereafter elevate the material to a higher temperature between 500 C. to 800 C. for a length of time such as is necessary to allow a small amount of the "gamma" phase to precipitate in ahighly dispersed form in the alpha Phase.

magnet material. This method of forming permanent magnet materials is different and seemingly involves a different principle than that heretofore employed with respect to many others, such as alloys of iron, cobalt and molybdenum, in that, in the present instance the material is converted into a low temperature "alpha" phase and thereafter has a small amount of the high temperature gamma phase precipitated therein in a fine and dispersed state. In the usual case of permanent magnets hardened by precipitation the high temperature phase is preserved and a small amount of the low temperature phase is precipitated.

In some alloys of the type under discussion the gamma" to alpha transformation tends to occur at low temperatures at which the transformation becomes sluggish and non-equilibrium conditions emst.

Whether this is the case or not, cold rolling these alloys in grooved. rolls or working them mechanically by any equivalent method causes or expedites the formation at room temperature of the alpha phase andbrings them into equilibrum. Some alloys of this type may not change completely to the "alpha phase at room temperature unless given the above treatment. By the rolling treatment others change to "alpha? phase only in part. 'Whether complete or partial this resultis one beneficial aspect of the present invention. However, there is a second beneficial aspect which is due to crystal orientation. X-ray measurements confirm this and magnetic tests show the best permanent magnet properties in the direction of elongation. Either or both of these beneficial aspects may be present in some degree.

After the alloys are brought into the "alpha" phase by the combination of cooling and cold working they are raised to atemperature which brings them into the temperature range which causes the preciptatlon in finely dispersed parof permanent magnet materials is the product of "coercive force" and residual induction." A

uct of induction B and magnetizing force H at a point where this product is the greatest. See Wahl, Applied Magnetism, pages 42 to 45, inclusive.

The above criterion is independent of the matter of cost, ease or difliculty of preparation, rolling or drawing, brittleness, availability of raw materialsand other factors which must receive consideration for many practical purposes and applications. Thus a permanent magnet composition which has an absolute maximum energy product less than some other which is less available or suitable from some one or more of the above aspects may be a valuable contribution to the art, if. for example, it may be made to possess a considerably greater maximum energy product. I

Among objects of the present invention are to provide better permanent magnets at little or no increase in cost; to produce useful permanent magnets from materials not hitherto known to possess permanent magnet properties to a useful extent; to improve the properties of compositions known to have useful permanent magnet properties; to produce useful permanent magnets from cheap or readily available raw materials, to increase either the product of "coercive force and "residual induction" or the fmaximum energy product" of magnetic materials; to provide elongated magnetic materials such as tapes and strips having useful magnetic properties; andto provide useful magnets from materials which may be worked with facility.

The subject-matter of the invention or discovery comprises a range or group of magnetic alloys which by appropriate combined heat treatment and cold rolling or elongating treatment will have one or the other or both of the abovenamed magnetic products or the coercive force or the residual induction increased'in the direction of elongation by from one hundred to severai hundred per cent as compared to the material in the cast or unsuitably heat treated or unsuitahly worked condition.

A feature of the invention or discovery isthe lack of any necessity for quenching the material in order to improve its properties; however, quenching may be practiced without ,detriment and one of the beneficial aspects of the discovery is that the cooling rate may vary widely as convenience or necessity demands.

The alloys may be prepared in. the form of rods, bars, wire or tapes. A suitable treatment for any specimen is first to give it the desired amount of cold working plus a low temperature bak'e. No other heat treatment is necessary. Satisfactory results have been obtained with reductions in area of 75 per cent, although this exact amount is by no means critical.

In greater detail, the material-is cast, which gives it the necessary high temperaturetreatment; it may be given a further or special heat treatment at around 800' C. to 1300 C. The cooled material, which may be cooled to room temperature slowly or rapidly and must be cooled substantially below about 600 C., is forcibly elongated by rolling with grooved rolls, swaging, drawing through dies or by combinations of these methods or by any similar method or methods so as to reduce the cross'section in one or several steps over a range from a small reduction to a reduction to a small fraction of the original cross section. The material is then heated to a temperature generally in the region 500' C. to 800 C. and maintained for a long time at the bottom of the range, one to several hours in the middle and much less if the temperature is at the top of the range. Too high a temperature destroys the effect of the cold rolling and too low a temperature or too short a time is only partially effective. A

quenching treatment is unnecessary.

A typical composition according to the invention as above-outlined is:

Percent Percent Percent iron manganese chromium Variations of the iron content within a range of to 85 per cent iron, manganese 12 to 18 per cent and chromium 2 to 8 per cent are within quenching.

These compositions exhibit substantial permanent magnet properties and are notably improved in properties by a treatment of the kind described. They may be prepared from raw materials which are ordinarily cheap and readily available. They respond .to the described treatment and to exhibit magnetic properties increased around 100 per cent or more as a resultv with the treatment described as compared with identical compositions as cast. The increase in energy product due to cold rolling alone may be considerably over 100 per cent as compared to the same material not cold rolled.

The apparatus illustrated inthe above-noted patent may be used to perform the cold rolling process.

The finished magnets are magnetized by the usual methods.

What is claimed is:

1. A permanent magnet consisting of '15 to as per cent iron, 12 to'18 per cent manganese, and 2 to 8 per cent chromium.

2. A cold rolled ma net consisting of '15 to 85 per cent iron, 12 to 18 per cent manganese, and 2 to 8 per cent chromium.

3. A magnet consisting of per cent iron, 16

. per cent manganese, and 4 per cent chromium.

4. An article having properties adapted for permanent magnet use composed of an alloy comprising as essential constituents '75 to per cent iron, 12 to 18 per cent manganese, and 2 to 8 per cent chromium, produced by causing the alloy to pass through or into the temperature range of from 800 C. to 1300", C., cooling it substantially.

into the temperature range of from 800 C. to 1300 0., cooling it substantially below 600 0., iorcibly elongating the material in the cold 'condition, and thereafter maintaining it in the range 500' C. to 800 C. without exceeding about 800 0., whereby the material is caused to have incooling the material to the general region of room temperature, forcibly elongating the material while cold, and thereafter maintaining it at 500 C. to 800 0., cooling it, and magnetizing it along the general axis of the direction of elongation.

7. The method of producing a permanent magnet which comprises composing an alloy of 80 per cent iron, 16 per cent manganese, and 4 per cent chromium, passing it into or through the temperature range 800C. to 1300 C., cooling the material to the general region of room temperature, forcibly elongating the material while cold, and thereafter maintaining it at 500 C. to 800 (L, cooling it, and magnetizing it along the general axis of the direction of elongation.

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